What is Obsessive Compulsive Disorder?

Obsessive Compulsive Disorder is one of the most common psychiatric disorders, affecting between two and three per cent of people. and can cripple their lives, disrupt learning, and drive a wedge through their families.

OCD has been called one of the 10 most disabling medical conditions worldwide by the World Health Organization.

The disorder is marked by persistent intrusive "bad" thoughts (the obsession), repetitive actions (the compulsion) and anxiety. The onset of disease often occurs during childhood.

Patients struggle with obsessions and the urgent need to repeat behaviours that can relieve anxiety. Sufferers may feel compelled to wash their hands or clean constantly with the hope of making obsessive thoughts go away, but such rituals provide only temporary relief.

The severity varies widely from person to person, and today's study confirms that genetics play a role. Earlier twin studies have shown identical twins have a higher incidence of OCD - almost 90 per cent - than fraternal twins, where the odds of both having the disorder is close to 50 per cent.

There are around two million sufferers in Britain, though this is an estimate since the average time taken from onset of the condition to diagnosis is around nine years, said Colin Putney of the charity OCD Action, himself a 49 year old sufferer.

OCD began in his case as compulsive hand washing and checking light switches, doors and windows as a child.